Investigation Of The Process And Properties Of Nano Porous Silicon-based Thin Film By Plasma Enhanced Vapour Deporsition At Atmospheric Pressure

The Si-based thin films with novel structure and photoluminescence (PL) emission wave length of 400nm were deposited using atmosphere plasma-enhanced chemical vapor deposition (APECVD).Dielectric-barrier discharges (DBD) equipment was self-designed and fabricated for the film deposition at atmospheric pressure. The properties of the equipment are simple, low power consumed. The plasma zone produced by the self-designed comb electrodes is uniform that is good to the film deposition. The process of the porous silicon deposition is a dry method which is proper to the photoelectric field and has some advantages over traditional way.The deposition process was discussed according to the analysis of the discharge parameters, including the voltage, current and power. The discharge frequency is 30-40kHz; voltage is 6-12kV; power is 2.6-4.0W. The relation between the optical emission spectrum and the deposition mechanism were discussed and the electron temperature was calculated.The wadding-like porous nanostructure silicon films were prepared with bias voltage, while the proportion of SiH₄/H₂/Ar gas mixture was 7.5L/min:30ml/min:15ml/min. The surface pattern was investigated by scanning electron microscope (SEM). The experiment results show that bias voltage has a great effect on formation of the nanostructure in the film. The structural defects in the porous silicon film have been investigated by using monoenergetic positrons beam technique. The results show that the defects were less under the bias voltage treatment and the defect species become simplified. The film chemical composition was confirmed by EDS; the characteristic peaks of FTIR transmittance spectrum were identified; the function groups were discussed by XPS.The photoluminescence (PL) spectrum of the porous silicon-based films was discussed. The emission wavelength of 400nm was observed and the emission peaks was concentrated in the blue and purple zone. The full wave at half maximum (FWHM) was large which means the photoluminescence has different kinds of emission mechanics. The Gaussian peak fitting results show that there are three main peaks in the photoluminescence: 3.15eV (393nm), 2.71eV (457nm) and 2.31eV (535nm). The relationship between the photoluminescence and the micro and nano structure was also discussed. And the photoluminescence intensity of the film had a long period of time. The mechanics of the PL was introduced and discussed. Quantum confinement effect and the oxygen atom are the main cause.